The three known Kazal isoinhibitors have been prepared in sufficient quantities to allow sequenation of each isoinhibitor. The sequence of A has been confirmed; B has Asp 1 instead of Asn 1; C has Asp 1 and Asp 14. an additional form, C', was isolated. It contained preferentially Asp 14-Gly 15 in beta linkage. Deamidation reactions occurred under surprisingly mild conditions. Swine colostrum inhibitors were separated into three classes: high molecular acidic inhibitor; a new class of low molecular acidic inhibitor; and the previously known low molecular basic inhibitors. An attempt was made to speed up the method of preparation of human alpha 1-PI by a minor modification of the method of Kurecki et al. reported last year. Additional electrophoretic bands visible on the gel containing purified alpha 1-PI were identified as polymers. The complex of alpha 1-PI with trypsin was prepared and products released from this complex were partially identified.